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Spawn several threads when we fail to enqueue work in the blocki… #181

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Merged
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Nov 1, 2019
Merged

Spawn several threads when we fail to enqueue work in the blocki… #181

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ee50156
Rebase onto master
Nov 1, 2019
20d39ef
Switch to unbounded channels
Nov 1, 2019
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46 changes: 25 additions & 21 deletions src/task/spawn_blocking.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,7 @@ use std::sync::atomic::{AtomicU64, Ordering};
use std::thread;
use std::time::Duration;

use crossbeam_channel::{bounded, Receiver, Sender};
use crossbeam_channel::{unbounded, Receiver, Sender};
use once_cell::sync::Lazy;

use crate::task::{JoinHandle, Task};
Expand Down Expand Up @@ -79,7 +79,7 @@ static POOL: Lazy<Pool> = Lazy::new(|| {
// before being acted on by a core. This helps keep
// latency snappy in the overall async system by
// reducing bufferbloat.
let (sender, receiver) = bounded(0);
let (sender, receiver) = unbounded();
Pool { sender, receiver }
});

Expand All @@ -95,27 +95,31 @@ fn maybe_create_another_blocking_thread() {
return;
}

// We want to avoid having all threads terminate at
// exactly the same time, causing thundering herd
// effects. We want to stagger their destruction over
// 10 seconds or so to make the costs fade into
// background noise.
//
// Generate a simple random number of milliseconds
let rand_sleep_ms = u64::from(random(10_000));
let n_to_spawn = std::cmp::min(2 + (workers / 10), 10);

thread::Builder::new()
.name("async-std/blocking".to_string())
.spawn(move || {
let wait_limit = Duration::from_millis(1000 + rand_sleep_ms);
for _ in 0..n_to_spawn {
// We want to avoid having all threads terminate at
// exactly the same time, causing thundering herd
// effects. We want to stagger their destruction over
// 10 seconds or so to make the costs fade into
// background noise.
//
// Generate a simple random number of milliseconds
let rand_sleep_ms = u64::from(random(10_000));

DYNAMIC_THREAD_COUNT.fetch_add(1, Ordering::Relaxed);
while let Ok(task) = POOL.receiver.recv_timeout(wait_limit) {
abort_on_panic(|| task.run());
}
DYNAMIC_THREAD_COUNT.fetch_sub(1, Ordering::Relaxed);
})
.expect("cannot start a dynamic thread driving blocking tasks");
thread::Builder::new()
.name("async-std/blocking".to_string())
.spawn(move || {
let wait_limit = Duration::from_millis(1000 + rand_sleep_ms);

DYNAMIC_THREAD_COUNT.fetch_add(1, Ordering::Relaxed);
while let Ok(task) = POOL.receiver.recv_timeout(wait_limit) {
abort_on_panic(|| task.run());
}
DYNAMIC_THREAD_COUNT.fetch_sub(1, Ordering::Relaxed);
})
.expect("cannot start a dynamic thread driving blocking tasks");
}
}

// Enqueues work, attempting to send to the threadpool in a
Expand Down